The tendency for 3-to 5-year-old children to use trait-relevant information about other people when evaluating aggressive responses to ambiguous behavior was examined across two studies (N = 81). Children were more likely to endorse the use of aggression against a "mean" versus a "nice" story character. Additionally, they were more likely to endorse the use of aggression against a story character who feels happy rather than sad when bad things happen to other kids. These findings suggest that, as early as preschool, trait-relevant information about other people can serve as a tool with which children evaluate the appropriateness of aggression in response to ambiguous behavior. Moreover, these findings provide evidence that even before the onset of formal schooling, trait and mental state information can influence social judgments.Keywords trait reasoning; social cognition; aggression; preschool; person perception Violence is a critical public health problem, one with great personal, social and economic costs [Cohen and Swift, 1993;Fontanarosa, 1995;Rosenberg et al., 1992]. It is becoming increasingly clear that violent behavior in adulthood has antecedents that are often evident early in development [see Coie and Dodge, 1998;Huesmann et al., 1984;Olweus, 1979]. There is a critical need to develop programs that successfully prevent violence, so a major goal of research on aggression is to determine the factors that are predictive of, and contribute to, aggressive behavior across development. Sociocognitive approaches to the study of childhood aggression have emphasized the important role that children's patterns of thinking play in supporting and maintaining aggressive behaviors [e.g., Huesmann and Guerra, 1997].One aspect of children's social cognition that has been of interest to researchers attempting to understand aggression in childhood is the extent to which children endorse, or approve of, the use of aggression as a means of responding to the provocations of others [Coie and Dodge, 1998;Giles and Heyman, 2003;Huesmann and Guerra, 1997;Henry et al., 2000; see also Erdley and Asher, 1998]. The tendency to endorse aggression has been linked to several negative behavioral outcomes, including increased levels of aggressiveness [Erdley and Asher, 1998;Huesmann and Guerra, 1997;Guerra and Slaby, 1989;Gouze, 1987], deficits in prosocial behavior [Erdley and Asher, 1998] 1985;Perry et al., 1986]. For example, Erdley and Asher [1998] found that fourth and fifth graders who believed strongly in the legitimacy of aggression as a means of solving problems were more aggressive and less prosocial than their peers.In addition to this evidence of individual differences, there is evidence that children tend to hold beliefs about aggression that are differentiated based on contextual factors, such as information about social actors [Dodge et al., 1984;Olthof et al., 1989, see also Giles and Heyman, in press]. For example, there is evidence that children's endorsement of aggression is affected by information about me...